P.R. Laws Ap. tit. 32A, § III, Rule 51.7
When a judgment is recovered against one or more of several debtors, jointly liable for an obligation, those debtors who are not parties to the action may be summoned to show cause why they should not be bound by the judgment in the same manner as if they had been originally sued. The summons, according to this rule, must describe the judgment, and require the person summoned to appear on a specific day and hour to show cause why he should not be bound by the judgment. It shall not be necessary to file a new complaint. The summons must be accompanied by an affidavit of the plaintiff, his agent, representative or attorney, stating that the judgment or some part thereof remains unsatisfied, and specifying the amount due thereon.
After service of the summons, the judgment debtor shall appear at the date specified thereon and at said hearing he may assert any defense of fact and of law that may release him from liability. Matters thus raised may be argued as in other cases.